There exists a need in many applications for a wakeup circuit to allow the remote initiation of power and control to a xe2x80x9cdormantxe2x80x9d accessory of a system without demanding from the user a separate step of system power initiation. There exists a further need to provide such a circuit that may operate without demanding a current draw associated with leaving the xe2x80x9cdormantxe2x80x9d system or accessory in a state of powered readiness or in a state of reduced power usage wherein a small current draw is maintained. There also exists a need in many applications for a safety circuit that is designed to provide a method for terminating the supply of power to the system or system accessories in the event that a microprocessor or other control unit fails, or in the event that a microprocessor or control unit loses contact with a remote accessory.
In passenger vehicles and especially in motor homes, luxury coaches, and recreational vehicles, the typical patterns of use involve periods of driving separated by extended periods of parked or stationary usage or extended periods of storage. In such vehicles, it is common for there to exist a large number of electrically powered or assisted accessories ranging from cooking amenities such as microwave ovens and refrigerators, to basic utilities such as lights, to entertainment equipment such as stereos and televisions, to starter engines for generators, etc. Further, it has become popular to provide powered, extendable or expandable rooms in such vehicles. Also, there have been introduced various power-controlled doors, steps and other slideable or extendible panels. Extendible rooms, for example, typically comprise a frame that is moveable between a retracted position, wherein a wall of the frame serves as an outer wall of the coach, to an extended position wherein the frame extends outwardly from the outer wall of the coach to serve as a sitting space, storage space, or other area convenient and appropriate for the chosen application. Numerous other power-controlled amenities or features are common including leveling systems or jacks to stabilize the vehicle when parked, and slide-out mechanical bays that provide easy access for maintenance and repairs.
In recreational vehicles, as in passenger vehicles, it is known to provide, through a separate power control panel, or more commonly through the ignition switch, a means for providing power to only select systems or subsystems within the vehicle. This practice is commonplace in passenger vehicles and light trucks wherein the radio, power windows, and other accessories may be provided with power by turning the ignition switch to an xe2x80x9caccessoryxe2x80x9d (or other appropriately named) setting that does not provide power, for example, to the starter engine, alarms, or other various non-selected systems. In this fashion, it is possible to have vehicle accessory systems that do not draw a current when they are not in use. However, as previously noted, it is necessary to supply power to these systems before they are placed in a state of readiness for use. Further, it is necessary to group these systems for shared use of a dedicated power switch or it is necessary to provide a plurality of power switches for the selected items.
In recreational vehicles which are commonly viewed as luxury items and which, of course, serve as homes for snowbirds, travelers, and professionals who must tour on a regular basis, it is desirable to provide maximum convenience. Given the size and the nature of use of such vehicles, operation of accessories frequently is desired when the operator is located remotely from the driver""s seat, for example, in the rear of the vehicle interior, at other spaces in the vehicle interior, or at locations on the exterior of the vehicle (if, for example, powered doors, or slide-out mechanical bays are accessed from the vehicle exterior). There is therefore a need to provide for convenient operation of accessories from the remote location. Given the length of periods during which such vehicles are parked or stored, there is also a need to conserve energy to prevent batteries from becoming drained. Therefore, the need to provide for convenient operation of accessories from a remote location is complicated by the need to provide a system that draws little or no current when in a dormant or waiting state.
The prior art includes various wakeup circuits wherein a system is provided with a standby or sleep mode in addition to a normal operating mode. An example from the area of vehicle systems is U.S. Pat. No. 5,216,674. As disclosed in the ""674 patent, it is known to provide a Controlled Area Network (CAN) circuit system in vehicle systems. In general terms, a CAN system or interface system connects via bus lines the numerous components, subsystems, and systems that form the substations of the CAN. CAN systems typically employ two communication lines for the movement of signals between a central control module and remotely distributed input/output modules. The ""674 patent discloses a particular wakeup circuit for a CAN vehicle system having a low power usage or low current draw sleep mode. Specifically, the wakeup circuit of the ""674 patent is described as having been designed to be operable even in the event that one of the two signal lines fails due to short circuit to ground or due to disturbance in voltage supply. However, at all times a fault detection current draw is present in the circuit of the ""674 patent.
In addition to the need for wakeup functionality, there also exists a need for an improved safety circuit designed to remove power to networked accessories in the event that the central control module or microprocessor fails or loses contact with an accessory. In many applications, for example, in the case of slide-out rooms in recreational vehicles or coaches, it is beneficial to provide as a safety feature a means for suspending power supplied to the slide out-room if power failure, communication failure, or microprocessor failure occurs. Therefore, the presently described invention includes circuits having wakeup functionality and circuits having safety or power suspension functionality. Although described with reference to vehicle-based application, it will be understood by those of ordinary skill in the art that the present invention is widely applicable beyond the field of vehicles and in many systems. The invention is of particular value in systems wherein energy conservation and/or safety-based power termination are important design considerations. Examples of applications for such systems are legion as the present invention relates broadly to the provision of the cited functionality.
The present invention relates generally to a wakeup circuit that allows remote initiation of power and control to a xe2x80x9cdormantxe2x80x9d accessory or system without demanding that system power be initiated in a separate step. The present invention also relates to a wakeup circuit that does not demand a quiescent or latent current draw by the system when in its dormant state. The present invention relates also to a safety circuit and to a safety circuit in combination with the wakeup circuit. The exemplary embodiment described herein relates specifically to a CAN type accessory or module system. However, the invention relates generally to other networked applications or network protocols and is not dependent upon the use of a CAN protocol.
In the wakeup circuit for providing power and control to a system accessory when that system accessory lies in a dormant state that may be characterized by zero current draw, a switch is provided at an operator""s panel or control panel for an accessory. Actuation of the accessory control switch provides a ground or reference voltage that, in effect, applies a ground xe2x80x9csignalxe2x80x9d to a wakeup wire. This ground connection is provided to a central control module (xe2x80x9cCCMxe2x80x9d) and the voltage difference exposed to the CCM from a power source and the ground causes current to flow to the CCM and xe2x80x9cwake-upxe2x80x9d the CCM. In turn, the networked accessories on the CAN system are powered in response to system power initiation through the CCM. From the user""s perspective, however, the accessory may respond and be powered merely by actuation of the control switch or mechanism. To accommodate the remotely activated xe2x80x9cwaking upxe2x80x9d of the CAN network, a xe2x80x9cwakeupxe2x80x9d wire, a controller power wire, and a controller ground wire are provided in a system trunk line in addition to the normal bus signal lines of the CAN system (typically comprising two shielded signal lines for communicating digital data and a xe2x80x9cdrainxe2x80x9d line or wire).
When the control or switch is released, the ground xe2x80x9csignalxe2x80x9d is not detected by the CCM. After a determined amount of time without ground signal detection, the CCM automatically powers down the system and the dormant state is resumed. In this manner, without a ground available in the quiescent circuit to drive current from the higher voltage power source, the system may lie in a dormant state that draws no current. If desired, or if appropriate for a selected application, a quiescent current draw may be allowed by circuit design. For example, an output driver or other element may be disposed to remain exposed to a current draw when the system is in a dormant state. Therefore, although it is an object of the present invention to provide a wakeup circuit for use with a system having a zero current draw dormant state, it is understood that the present invention also encompasses those circuits that permit a small quiescent draw due to slight variations or deviation from the circuit described herein.
The safety circuit, which is described herein in combination with the wakeup circuit, and separately, comprises an AC source, preferably a first and a second operational amplifier, having output current feeds provided to opposite sides of a non-polarized capacitor and an AC relay coil arranged in series. In a state of normal operation, the safety circuit amplifier produces an AC current from an intermittent DC source. Because the capacitor will only pass AC current, catastrophic failure by the microprocessor, or other event that terminates exposure of the first operational amplifier to the DC source will also terminate the AC current across the AC control relay 30. Therefore, the capacitor appears to the system to be an open circuit and the coil of the AC control relay 30, which allows a normally open relay contact used to supply output drivers and the CAN bus modules, falls open terminating power to output drivers and causing other contacts to fall open and terminate power to the microprocessor. Generally therefore, the safety circuit comprises an input, an AC source, and a capacitor in series with an electrically operated, AC sensitive switch.